Swan Piston Seal

April 28, 2012

A few weeks ago I acquired a Swan Capacity Pen. Which is a US made, 1934 (or so) type of piston filler. I have finally completed the disassembly, it was a bear, involving creating some specialized tools to get places in the barrel. I will post a write up on the innards in the future if anyone is interested.

What I am looking for is an idea of what to replace the piston gasket with. The original, in the photo below, seems to be a rubber product (red) with felt wrapped around it (likely soaked in silicone?) I would like to replace it with something similar. I considered o-rings but since the inside of the barrel is flattened on two sides I think the o-rings would put undue pressure on the flat guides. Cork? Well I don't have the capacity to cut cork seals and I'm pretty sure that I could not get them to the correct tolerance if I did.

Is the original material a known entity that was commonly used on other Mabie Todd products? Or is this, as I suspect, something I will have to make up building up a substrate which I wrap felt around, silicone up and see if it holds? Or does someone else have a clever idea that I haven't thought of yet.

Thanks!

--greg

The photo shows the gasket material which sits in the middle of the hourglass shaped piston. The piston rides on the helical screw and stays aligned in the barrel via the flat spots on either side of piston (better illustrated in the second photo).

http://farm8.staticflickr.com/7083/7122774439_a27a4a65bc_z.jpg

http://farm9.staticflickr.com/8020/6976692670_b1b02f702a_z.jpg

May 3, 2012

Any luck? The only thing I can think of is two o-rings, one at each hourglass end, then some built up material with silicone soaked felt inbetween

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O-ring, felt, o-ring

May 3, 2012

Thanks for asking SigmaZuiko,

I understand what you are saying. I'm waiting on felt right now, then I will hit the hardware store to see if there is any inspiration. I may take the o-ring idea and use a series of them behind the felt as a spacer. I also think I may try molding a back-spacer with silicone caulk unless I can find something that already exists that I could modify. Whatever I end up with I think it needs to be spongy to properly seal to the inner circumference of the barrel.

--greg

Any luck? The only thing I can think of is two o-rings, one at each hourglass end, then some built up material with silicone soaked felt inbetween

|()[]()|

O-ring, felt, o-ring

August 3, 2012

For those who are interested this is an update on the repair of the Swan Capacity Pen referred to above and in this post. From what I understand the Capacity Pen is not common though it is not very desirable either. I didn't pay a whole lot for it and since I enjoy tinkering it seemed to be a good project. It's still missing the clip which I would be interested in finding some day.

The pen now functions reasonably well with regard to ink intake and output. I haven't yet spent the time figuring out how much ink the Capacity Pen actually holds but it seemed about the same as most smaller Vac-fil pens that I own.

I had very little to go on with regards to the repair but wanted to provide an exploded view of the major parts and a diagram of how I think it works:

(I have transcribed some of the names between the two drawings which I understand might be confusing, I apologize for that)

How I think the pen works:

The filling knob turns a helical threaded tube which advances and retracts a packing carrier (truck), in turn this draws ink through the nib and feed channels. Air above the carrier is expelled through a hole at the top of the helical tube and out a hole in the back side of the feed (opposite the ink channel). The carrier tracks because inside diameter of the barrel is flattened on two sides, as is the carrier.

The filler knob is made up of several concentric parts (not sure why) that are held together by a pin. I did not try to disassemble this, the pin only goes partway into the barrel and seemed to be glued in place. There was no way I could see to knock it out, nor was there any need to. The center of the knob has a square hole into which fits the square end of the helical tube.

The packing carrier itself is hourglass shaped with threaded hole in the middle to travel on the shaft. I am guessing that is it constructed of hard rubber and would be one of the most difficult parts to manufacture. I replaced the packing material with a small layer of silicone from a sac then wrapped high quality, silicone soaked felt. I shaped the felt to meet at an angle to cause the pressure of the barrel to help hold the ends of the felt air tight. i.e. : ---//---

This photo shows the old packing material:

There is what I assume to be a shaft bearing that keeps the shaft centered in the barrel. The packing carrier is kept in the barrel by a "stop nut" which threads into the barrel up to the shaft bearing. The hole in the middle is slightly bigger than the shaft allowing ink to pass. I "machined" a "split slot" screwdriver to remove this hard rubber nut.

The helical shaft tube and the "stop nut", the shaft bearing is right behind the flat nut:

The nut removal tool, ground down with a set of hand files, I have no grinder.

The bearing (metal bit with wings) and the Stop Nut.

It was more difficult to figure out how to remove the carrier since I didn't really know how it was fastened. Ended up using a piece of guitar string bent at the ends, slid down the flat sides of the carrier (at this end of the barrel it's round so there was just enough room), lightly pulled while rotating the filler knob. It came right out. Next time I would know to just carefully pull on the shaft and the carrier and shaft will disengage from the inside of the filler knob. The carrier is intended to be threaded on to the shaft on the filler end.

Carrier on the shaft with the removal tool:

Carrier removal tool:

The section assembly has a hole in the middle of the feed to receive the shaft which seems to have been tapered to allow a tight fit. The hole in the "top" of the feed leads directly to the hole in the back of the feed, which again allows air to pass behind the carrier.

Nib Assembly showing a crude sketch of the back view and barrel end:

One thing I had trouble with is seeing how the space between the carrier and the shaft sealed, I'm not sure I figured it out. At first I had trouble getting the pen to fill, so I packed the center of the hourglass carrier with silicone grease and then it seemed to fill just fine. If anyone sees and errors or omissions please let me know, I would be happy to correct it or answer any questions.

--greg, amateur pen fixer

August 3, 2012

Fascinating repair journey! I love the pen specifically for its exotic innards! Very much enjoyed your diagrams and commentary on the evolution of your thinking towards resolving the issue. Thank you for sharing.